The present invention is directed to an improved power and free conveyor trolley construction and method of construction wherein malleable axles for attaching wheels are incorporated into a cast trolley body.
Power and free conveyor systems are in wide-spread use for transporting parts, goods under construction, finished goods, etc. The component, which has made conveyor systems so useful, is commonly referred to as a trolley. A trolley includes a body typically supported on wheels or rollers which are mounted on axles generally transverse to the trolley bodies. Many of the applications for power and free conveyor systems include automobile assembly lines and other types of assembly requiring the support and transport of relatively heavy parts or completed products by the conveyor system. As a result, trolleys are very often subjected to the requirement of conveying and transporting substantial loads. Heavy duty trolleys of this type can be expensive to construct.
One approach commonly used to minimize fabrication costs of the trolley bodies has been to cast the bodies for trolleys with integral laterally extending projections for the axles. The projections are subsequently machined to the size and shape required to mate with the wheels and then secured to an inner race of a wheel to complete construction of the trolley. The major problem with this approach, however, is that the materials which can be formed from a cast molten process are normally not sufficiently malleable or machinable to allow swaging or other operations that provide for easy attachment of the wheel and also do not have the more desirable high strength characteristics preferred for this type of application. As a result, trolleys manufactured by this process are relatively shortlived, which results in reduced reliability, frequent maintenance and potentially substantial downtime for an assembly line which depends on power and free conveyor systems.
An approach which has been used to improve the lifetime of the trolleys is to pour or cast the trolley bodies as described with the preceding approach but without the integral laterally extending projections. After casting, the trolley bodies are precision machined and bores are drilled to receive preformed axles made of high strength steel which more readily meet the requirements of extended performance and reduced maintenance. Unfortunately, the precision machining and the pressing of the preformed axles into the trolley bodies substantially increases the manufacturing costs thereof and the axles may work loose from the body associated therewith.
A technology now exists for a material--austempered ductile iron ("ADI")--which exhibits a wider range of properties than any other engineering material presently available for constructing trolley bodies. The present invention provides the ability to incorporate high strength machinable steel axles into a cast trolley body constructed of austempered ductile iron while eliminating the high costs associated with the subsequent machining and pressing processes.